Zinc binding (ZB) domains are found in numerous proteins which are involved in protein-nucleic acid or protein-protein interactions. ZB proteins are commonly involved in the regulation of gene expression, and may serve as transcription factors and signal transduction molecules. A ZB domain is generally composed of 25 to 30 amino acid residues which form one or more tetrahedral ion binding sites. The binding sites contain four ligands consisting of the sidechains of cysteine, histidine and occasionally aspartate or glutamate. The binding of zinc allows relatively short stretches of polypeptide to fold into defined structural units which are well-suited to participate in macromolecular interactions (Berg, J. M. et al. (1996) Science 271: 1081-1085).
Classes of ZB domains are characterized according to the number and positions of the residues involved in the zinc atom coordination. ZB domains which contain a C.sub.3 HC.sub.4 sequence motif are known as RING domains (Lovering, R. et al. (1993) Proc. Natl. Acad. Sci. 90: 2112-2116). The RING domain binds two zinc ions in an arrangement structurally different from that of the zinc finger. The RING domain consists of eight metal binding residues, and the sequences that bind the two metal ions overlap (Barlow, P. N. et al. (1994) J. Mol. Biol. 237: 201-211). The consensus sequence C-X.sub.2 -C-X.sub.(9-27) -C-X.sub.(1-3) -H-X.sub.(2-3) -C-X.sub.2 -C-X.sub.(4-48) -C-X.sub.2 -C provides for loops of varying length which form the overlapping Zn binding sites. The two Zn binding sites are formed by four pairs of metal-binding Cys and His residues. The first and third pairs bind one metal ion, while the second and fourth pairs bind the other (Barlow, et al., supra). Functions of RING finger proteins are mediated through DNA binding and include the regulation of gene expression, DNA recombination, and DNA repair.
The murine BMI-1 gene encodes a protein of 324 amino acids. This protein, which is found in the nuclei of a variety of normal cells, contains a RING domain near the amino-terminus (Haupt, Y. et al. (1991) Cell 65: 753-763). Retroviral insertional mutagenesis of E-mu/myc transgenic mice by infection with Moloney murine leukemia virus (MuLV) accelerates development of B lymphoid tumors. In about half of independently induced pre-B-cell lymphomas, the provirus integrates in or near the BMI-1 gene and causes enhanced transcription of BMI-1. Haupt et al. (supra) concluded that myc-induced lymphomagenesis may entail the concerted action of several genes including the putative nuclear regulator BMI-1.
The human BMI-1 gene encodes a protein of 326 amino acids which shares 98% identity to the mouse amino acid sequence (Alkema, M. J. et al. (1993) Hum. Mol. Genet. 2: 1597-1603). Fluorescence in situ hybridization (FISH) on metaphase chromosome spreads localized the human BMI-1 proto-oncogene to the short arm of chromosome 10 (10p13), a region known to show translocations and to be involved in various leukemias (Alkema et al., supra).
The breast and ovarian cancer susceptibility-1 (BRCA1) gene encodes a predicted protein of 1,863 amino acids which contains a RING domain in its amino-terminal region (Miki, Y. et al. (1994) Science 266: 66-71). BRCA1 is expressed in numerous tissues including breast and ovary. In sporadic breast cancer, BRCA1 mRNA levels are markedly decreased during the transition from carcinoma in situ to invasive cancer (Thompson M. E. et al. (1995) Nature Genet. 9: 444-450). Furthermore, experimental inhibition of BRCA1 expression with antisense oligonucleotides produced accelerated growth of normal and malignant mammary cells but had no effect on nonmammary epithelial cells. Thompson et al. (supra) suggest that BRCA1 may normally serve as a negative regulator of mammary epithelial cell growth and that this function is compromised in breast cancer either by direct mutation or by alterations in gene expression.
The chicken zinc RING protein, C-RZF, is 381 amino acids in length. Its expression occurs as a consequence of the binding of cytotactin/tenascin (CT/TN), a substrate adhesion molecule, to chicken embryo brain cells (Tranque, P. et al. (1996) Proc. Natl. Acad. Sci. 93: 3105-3109). In addition to the RING zinc-binding motif, C-RZF also contains a leucine zipper, a nuclear localization signal, and an acidic transcription activation domain. These results suggest that C-RZF binds DNA and functions as a transcription regulator in response to a signal transduction network related to the CT/TN expression. Alternatively, C-RZF may function in communication between cell adhesion events at the cell membrane and changes in the nucleus, which regulates cell shape, migration, or differentiation (Tranque et al., supra).
The discovery of a new human zinc RING protein and the polynucleotides encoding it satisfies a need in the art by providing new compositions which are useful in the diagnosis, prevention and treatment of inflammation and disorders associated with cell proliferation and apoptosis.